1. Field of the Invention
The present invention relates to a linear actuator and a vacuum control device for use with a vacuum chamber in which plasma is generated.
2. Description of the Related Art
Manufacturing semiconductor devices involves a process which uses plasma; for example, plasma etching. In the plasma etching process, for example, a vacuum control valve controls a vacuum pressure in a vacuum chamber while allowing etching gas to flow. A vacuum is controlled through adjustment of conductance of the vacuum control valve. In the case of a pendulum-type vacuum control valve used widely in plasma etching, valve opening is adjusted through operation of a pendulum-type valve body, thereby adjusting conductance (Japanese Patent Application Laid-Open (kokai) No. 2009-117444). However, since controllability of operation of the pendulum-type valve body is low in a low flow rate region (low conductance region), the pendulum-type vacuum control valve involves a problem of failure to cope with a low flow rate of etching gas. Meanwhile, a poppet-type vacuum control valve which copes with a low flow rate of etching gas is conventionally used to control a vacuum. The poppet-type vacuum valve is configured such that a valve body is attached to a piston (moving member) of a linear actuator. Through control of the distance between the valve body and a valve seat (lift), conductance is adjusted (Japanese Patent Application Laid-Open (kokai) No. 2010-276096). The linear actuator employed in the poppet-type vacuum control valve uses bellows for sealing a slide section of the piston. Since the bellows is made of metal and, thus, does not have plasma resistance, difficulty is encountered in using the poppet-type vacuum control valve in a vacuum chamber which handles plasma. Japanese Patent Application Laid-Open (kokai) No. 2003-194257, Japanese Patent Application Laid-Open (kokai) No. 2000-130635, and Japanese Patent Application Laid-Open (kokai) No. H03-260072 also describe a valve apparatus.